Modern radio-frequency (RF) devices such as radar range and velocity sensors or wireless communication devices can be integrated in integrated circuits (ICs, e.g. monolithic microwave integrated circuits, MMICs).
Such ICs may incorporate all core functions of an RF frontend (e.g. local oscillator, power amplifiers, low-noise amplifiers (LNA), mixers, etc.), the analog preprocessing of the intermediate frequency (IF) or base band signals (e.g. filters, amplifiers, etc.), and the analog-to-digital conversion in one single package.
Exemplary applications of such integrated circuits are frequency-modulated continuous-wave (FMCW) radar systems that make use of RF signals whose frequency is modulated by ramping the signal frequency up and down. Such RF signals are often referred to as “chirp signals” or simply as chirps, wherein frequency is ramped up in an up-chirp and ramped down in a down-chirp. For generating such chirp signals the radar transmitter may include a local oscillator (LO), which includes a voltage-controlled oscillator (VCO) connected in a phase-locked loop (PLL).
The quality of the LO signal may affect the quality and/or reliability of the IC's operation. For some applications, the VCO included in an IC may be tested, for example during an end-of-line (EOL) test during production or regularly during operation of the IC. The power of the phase noise of a VCO is one quality parameter that affects the signal-to-noise ratio of the generated RF signals. In order to be able to test parameters like the phase noise power generated by an integrated VCO an IC may include specific circuits, circuit components or other features that enable the testing of the VCO in order to check whether the VCO can operate in accordance with desired specifications.